For vs. For Each

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

This was discussed a time ago and U think remember that there were almost
no differences,
beside that, this is VERY EASY to check just write an small program and
iterate both ways and see the results

and finally this is a VB.net question, not a C# one, there is no need to
post it on microsoft.publi c.dotnet.langua ges.csharp

cheers,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation
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news:OY******** ******@TK2MSFTN GP11.phx.gbl...

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

[Joris Dobbelsteen]

In VB6 for a Collection you should use 'for each'. Here (.NET) it probably
doesn't matter.

I suppose you should use 'for each', because its cleaner and might use
optimizations whenever this will be possible. IHMO it looks cleaner too.

- Joris

<an*******@disc ussions.microso ft.com> wrote in message
news:OY******** ******@TK2MSFTN GP11.phx.gbl...

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

[One Handed Man \( OHM - Terry Burns \)]

There should be very little in the way of performance difference in these
two code snippets, especially as your control numbers are not likely to be
large anyway.

One point to note is that with For Each, you cannot remove the items or add
to the collection while iterating otherwise it complains, however with a for
loop, you can iterate backwards and remove items.


--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
If U Need My Email ,Ask Me

Time flies when you don't know what you're doing

<an*******@disc ussions.microso ft.com> wrote in message
news:OY******** ******@TK2MSFTN GP11.phx.gbl...

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

[Gabriele G. Ponti]

Anders Hejlsberg: "Generally my answer is, Always use FOR EACH if you can,
because chances are you will have fewer bugs if you use FOR EACH. There are
just more pitfalls with the regular FOR statement. It is true that in some
cases the FOR statement is more efficient. I think the vast majority of
cases, I don’t think you would ever notice. My advice would be, always use
FOR EACH profile your app. If they turn out to be your problem, then change
them to FOR statements, but I don’t think you ever will in real code. I
think FOR EACH is much more expressive, and in theory allows us to optimize
your code more in the future. There are certain optimizations that we will
do, because we can tell that you’re going over the entire collection or
whatever, and so we could, at least in theory, generate even better code. I
would highly recommend FOR EACH unless you really do need the index."

http://msdn.microsoft.com/msdntv/epi...h/manifest.xml

[Jay B. Harlow [MVP - Outlook]]

Eric,
In addition to the other comments:

Are you asking about the Controls collection specifically or are you asking
any collection in general?

As each collection type has its own performance characteristics !
(ControlCollect ion, verses ArrayList, verses Collection, verses an Array,
verses HashTable, verses insert your favorite collection here).

I have to ask: Does it really matter which is faster?

I would not worry about which performs better, I would go with which one is
more straight forward, I find the For Each more straight forward, so that is
the one I favor.

Remember that most programs follow the 80/20 rule (link below) that is 80%
of the execution time of your program is spent in 20% of your code. I will
optimize (worry about performance) the 20% once that 20% has been identified
& proven to be a performance problem via profiling (CLR Profiler is one
profiling tool).

For info on the 80/20 rule & optimizing only the 20% see Martin Fowler's
article "Yet Another Optimization Article" at
http://martinfowler.com/ieeeSoftware...timization.pdf

Hope this helps
Jay

<an*******@disc ussions.microso ft.com> wrote in message
news:OY******** ******@TK2MSFTN GP11.phx.gbl...

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

[Nick Malik]

Would you have been happier if Eric has written the question in C#? This is
very much as important a question in C# as it is in VB.NET.

foreach (Control ctl in myObject.Contro ls)
{
// do something useful with 'ctl'

}

I've had folks tell me that 'for' is more efficient than 'foreach' because
of enumerator overhead. For most of my code, however, this is a moot point.
Unless the code is in a critical loop, the difference in processing so tiny
that the improvement in code readability greatly outweighs the overhead of
allowing .NET to manipulate the enumerator.

--- Nick

"Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us > wrote
in message news:%2******** **********@TK2M SFTNGP11.phx.gb l...
<<clipped>>

and finally this is a VB.net question, not a C# one, there is no need to
post it on microsoft.publi c.dotnet.langua ges.csharp
<<clipped>>
<an*******@disc ussions.microso ft.com> wrote in message
news:OY******** ******@TK2MSFTN GP11.phx.gbl...

Is there a performance difference between this:

\\\
Dim i As Integer
For i = 0 to myObject.Contro ls.Count - 1
myObject.Contro ls(i) = ...
Next
///

and this:

\\\
Dim ctl As Control
For Each ctl In myObject.Contro ls
ctl = ...
Next
///

Or is For Each just "prettier"?

Thanks,

Eric

Jay B. Harlow [MVP - Outlook] wrote:

Are you asking about the Controls collection specifically or are you asking any collection in general?
As each collection type has its own performance characteristics !
I just meant collections in general, but you make a good point.
I have to ask: Does it really matter which is faster?
Not on my current projects, but it's good to know for the future.
Remember that most programs follow the 80/20 rule (link below) that is 80%
of the execution time of your program is spent in 20% of your code. I will
optimize (worry about performance) the 20% once that 20% has been identified & proven to be a performance problem via profiling (CLR Profiler is one
profiling tool).

I usually follow the 80/20/100 rule, where I optimize the 20% and give the
remaining 80% a good work over anyway to make sure the aggregate is as
efficient as possible. ;-)

Thanks for your reply, Jay.

Eric

Thanks for the post, Nick.

Nick Malik wrote:

I've had folks tell me that 'for' is more efficient than 'foreach' because
of enumerator overhead.

A newbie question...Wher e do enumerators come into play when using For Each?
In addition , since enumerators can only be of type byte, short, int, or
long, what kind of overhead is introduced?

Thanks again,

Eric

[One Handed Man \( OHM - Terry Burns \)]

He is referring to the Enumerator Interface IEnumerator. See below, you can
create your own.

Public Class Class1
Implements IEnumerator

Public ReadOnly Property Current() As Object Implements
System.Collecti ons.IEnumerator .Current
Get

End Get
End Property

Public Function MoveNext() As Boolean Implements
System.Collecti ons.IEnumerator .MoveNext

End Function

Public Sub Reset() Implements System.Collecti ons.IEnumerator .Reset

End Sub
End Class

--

OHM ( Terry Burns )
. . . One-Handed-Man . . .
If U Need My Email ,Ask Me

Time flies when you don't know what you're doing

<an*******@disc ussions.microso ft.com> wrote in message
news:%2******** **********@TK2M SFTNGP10.phx.gb l...

Thanks for the post, Nick.

Nick Malik wrote:

I've had folks tell me that 'for' is more efficient than 'foreach' because of enumerator overhead.
A newbie question...Wher e do enumerators come into play when using For

Each? In addition , since enumerators can only be of type byte, short, int, or
long, what kind of overhead is introduced?

Thanks again,

Eric